Listener的簡單介紹及使用

一、Listener概述

Listener可以監聽容器中某一執行動作，並根據其要求做出相應的響應。   
常用的Web事件的監聽接口如下：
ServletContextListener：用於監聽Web的啓動及關閉
ServletContextAttributeListener：用於監聽ServletContext範圍內屬性的改變
ServletRequestListener：用於監聽用戶請求
ServletRequestAttributeListener：用於監聽ServletRequest範圍屬性的改變
HttpSessionListener：用於監聽用戶session的開始及結束
HttpSessionAttributeListener：用於監聽HttpSession範圍內的屬性改變

二、ServletContextListener的使用

1、配置web.xml（下面例子都使用此配置文件）

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" 
    xmlns="http://java.sun.com/xml/ns/javaee" 
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
    http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
  <!-- 初始化參數 -->
  <context-param>
      <param-name>driver</param-name>
      <param-value>com.mysql.jdbc.Driver</param-value>
  </context-param>
  <context-param>
       <param-name>url</param-name>
       <param-value>jdbc:mysql://localhost:3306/escshop</param-value>
  </context-param>
  <context-param>
       <param-name>user</param-name>
       <param-value>root</param-value>
  </context-param>
  <context-param>
        <param-name>pass</param-name>
        <param-value></param-value>
  </context-param>
  <!-- 定義Filter -->
  <filter>
     <filter-name>logFilter</filter-name>
     <filter-class>Filter.LogFilter</filter-class>
  </filter>
  <!-- 定義Filter攔截的URL地址 -->
  <filter-mapping>
      <filter-name>logFilter</filter-name>
      <!-- 負責攔截的URL，/*表示攔截所有的請求 -->
      <url-pattern>/*</url-pattern>
  </filter-mapping>
  <!-- 定義AuthorityFilter -->
  <filter>
      <filter-name>authority</filter-name>
      <filter-class>Filter.AuthorityFilter</filter-class>
      <init-param>
          <param-name>encode</param-name>
          <param-value>UTF-8</param-value>
      </init-param>
      <init-param>
          <param-name>indexPage</param-name>
          <param-value>/index.jsp</param-value>
      </init-param>
      <init-param>
           <param-name>shopPage</param-name>
           <param-value>/shop.jsp</param-value>
      </init-param>
  </filter>
  <filter-mapping>
      <filter-name>authority</filter-name>
      <url-pattern>/*</url-pattern>
  </filter-mapping>
  <!-- 登錄servlet -->
  <servlet>
       <servlet-name>LoginServlet</servlet-name>
       <servlet-class>Login.LoginServlet</servlet-class>
       <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
        <servlet-name>LoginServlet</servlet-name>
        <url-pattern>/login</url-pattern>
  </servlet-mapping>
  <!-- 配置監聽Web啓動與關閉的Listener -->
  <listener>
      <listener-class>listener.GetConnListener</listener-class>
  </listener>
  <!-- 用於監聽ServletContenxt(application)範圍的變化 -->
  <listener>
      <listener-class>listener.MyServletContenxtAttributeListener</listener-class>
  </listener>
  <!-- 用於監聽用戶請求到達 -->
  <listener>
      <listener-class>listener.RequestListener</listener-class>
  </listener>
  <listener>
      <listener-class>listener.OnlineRequestListener</listener-class>
  </listener>
  <!--用戶監聽用戶session創建與銷燬  -->
  <listener>
      <listener-class>listener.OnlineListener</listener-class>
  </listener>
</web-app>

2、使用ServletContextListener

package listener;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

import javax.servlet.ServletContext;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
/**
 * 監聽Web應用啓動及關閉
 * @author xieyongxue
 *
 */
public class GetConnListener implements ServletContextListener{
    //應用關閉時，此方法被調用
    public void contextDestroyed(ServletContextEvent sce) {
        // TODO Auto-generated method stub
        ServletContext application=sce.getServletContext();
        Connection conn=(Connection) application.getAttribute("conn");
        if (conn!=null) {
            try {
                conn.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
    //應用啓動時，此方法被調用
    public void contextInitialized(ServletContextEvent sce) {
        // TODO Auto-generated method stub
        //獲取到該應用的ServletContext的實例
        ServletContext application=sce.getServletContext();
        //獲取數據庫驅動
        String driver=application.getInitParameter("driver");
        //加載數據庫連接URL
        String url=application.getInitParameter("url");
        //獲取登錄數據庫的名稱
        String user=application.getInitParameter("user");
        //獲取連接數據庫的密碼
        String pass=application.getInitParameter("pass");
        try {
            try {
                Class.forName(driver);
            } catch (ClassNotFoundException e) {
                // TODO Auto-generated catch block
                System.out.println("加載數據庫驅動失敗！"+e.toString());
                e.printStackTrace();
            }
            Connection conn= DriverManager.getConnection(url, user, pass);
            //將數據庫連接設置成application的屬性
            application.setAttribute("conn", conn);
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            System.out.println("連接數據庫失敗！"+e.toString());
            e.printStackTrace();
        }
    }
}

3、使用ServletContextAttributeListener

package listener;
import javax.servlet.ServletContext;
import javax.servlet.ServletContextAttributeEvent;
import javax.servlet.ServletContextAttributeListener;
public class MyServletContenxtAttributeListener implements ServletContextAttributeListener{
    //當程序向application範圍新增屬性時觸發此方法
    public void attributeAdded(ServletContextAttributeEvent scab) {
        // TODO Auto-generated method stub
        ServletContext application=scab.getServletContext();
        //獲取新增的屬性名與值
        String name=scab.getName();
        Object value=scab.getValue();
        System.out.println(application+"範圍內新增了name值爲="+name+"value值="+value);
    }
     //當程序向application範圍移除屬性時觸發此方法
    public void attributeRemoved(ServletContextAttributeEvent scab) {
        // TODO Auto-generated method stub
        ServletContext application=scab.getServletContext();
        //獲取移除的屬性名與值
        String name=scab.getName();
        Object value=scab.getValue();
        System.out.println(application+"範圍內移除了name值爲="+name+"value值="+value);

    }
    //當程序向application範圍替換屬性時觸發此方法
    public void attributeReplaced(ServletContextAttributeEvent scab) {
        // TODO Auto-generated method stub
        ServletContext application=scab.getServletContext();
        //獲取替換的屬性名與值
        String name=scab.getName();
        Object value=scab.getValue();
        System.out.println(application+"範圍內替換了name值爲="+name+"value值="+value);
    }
}

4、測試例子

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
application.setAttribute("addAttrName","addAttrValue");
application.removeAttribute("addAttrName");
application.setAttribute("newAttrName","newAttrValue");
application.setAttribute("newAttrName","1234567");
request.setAttribute("requestName1","requestValue1");
request.removeAttribute("requestName1");
request.setAttribute("requestName2","requestValue2");
request.setAttribute("requestName2","requestValue23");
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">
    <title>Login</title>
    <meta http-equiv="pragma" content="no-cache">
    <meta http-equiv="cache-control" content="no-cache">
    <meta http-equiv="expires" content="0">    
    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
    <meta http-equiv="description" content="This is my page">
  </head>
  <body>
    ${tip}<br>
    <form action="login?action=service" method="post">
                    名稱:<input type="text" name="user"><br>
                    密碼:<input type="text" name="pass"><br/>
      <input type="submit" value="登錄"><input type="reset" value="重置">
    </form>
  </body>
</html>

二、使用HttpSessionListener統計用戶在線人數

1、實現HttpSessionListener監聽器
package listener;
import java.util.HashMap;
import java.util.Map;
import javax.servlet.ServletContext;
import javax.servlet.ServletRequest;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
public class OnlineListener implements HttpSessionListener{
    //當用戶與服務器開始session時觸發該方法
    public void sessionCreated(HttpSessionEvent se) {
        // TODO Auto-generated method stub
        HttpSession session=se.getSession();
        ServletContext application=session.getServletContext();
        //獲取sessionId
        String sessionId=session.getId();
        session.setMaxInactiveInterval(15);
        //如果是新連接
        if(session.isNew()){
            Map<String,String> online=(Map<String, String>) application.getAttribute("online");
            String user=(String) session.getAttribute("user");
            user=(user==null?"遊客":user);
            if(online==null){
                online=new HashMap<String, String>();
            }
            online.put(sessionId, user);
            application.setAttribute("online", online);
        }   
    }
    //當用戶與服務器斷開session時觸發該方法
    public void sessionDestroyed(HttpSessionEvent se) {
        // TODO Auto-generated method stub
        HttpSession session=se.getSession();
        ServletContext application=session.getServletContext();
        String sessionId=session.getId();
        System.out.println("sessionId:"+sessionId);
        HashMap<String,String> online=(HashMap<String, String>) application.getAttribute("online");
        if(online!=null){
            online.remove(sessionId);
        }
        application.setAttribute("online",online);
    }
}

2、登錄控制器
package Login;
import java.io.IOException;
import java.util.HashMap;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
public class LoginServlet extends HttpServlet{
    public void service(HttpServletRequest request,HttpServletResponse response)throws ServletException,IOException{
        String user=request.getParameter("user");
        String pass=request.getParameter("pass");
        HttpSession session=request.getSession();
        //session.setMaxInactiveInterval(3);
        session.setAttribute("user", user);
        session.setAttribute("pass", pass);
        ServletContext application=session.getServletContext();
        HashMap<String,String> dataMap=(HashMap<String, String>) application.getAttribute("online");
        if(dataMap==null){
            dataMap=new HashMap<String, String>();
        }
        dataMap.put(session.getId(),user);
        application.setAttribute("online", dataMap);
        try {
            //轉發
            //request.getRequestDispatcher("/shop.jsp").forward(request, response);
            //重定向
            System.out.println("user1:"+session.getAttribute("user"));
            response.sendRedirect("/webPrj/shop.jsp");
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

3、登錄界面
<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
application.setAttribute("addAttrName","addAttrValue");
application.removeAttribute("addAttrName");
application.setAttribute("newAttrName","newAttrValue");
application.setAttribute("newAttrName","1234567");
request.setAttribute("requestName1","requestValue1");
request.removeAttribute("requestName1");
request.setAttribute("requestName2","requestValue2");
request.setAttribute("requestName2","requestValue23");
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">
    <title>Login</title>
    <meta http-equiv="pragma" content="no-cache">
    <meta http-equiv="cache-control" content="no-cache">
    <meta http-equiv="expires" content="0">    
    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
    <meta http-equiv="description" content="This is my page">
  </head>
  <body>
    ${tip}<br>
    <form action="login?action=service" method="post">
                    名稱:<input type="text" name="user"><br>
                    密碼:<input type="text" name="pass"><br/>
      <input type="submit" value="登錄"><input type="reset" value="重置">
    </form>
  </body>
</html>
4、在線用戶顯示
<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">
    <title>My JSP 'shop.jsp' starting page</title>
    <meta http-equiv="pragma" content="no-cache">
    <meta http-equiv="cache-control" content="no-cache">
    <meta http-equiv="expires" content="0">    
    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
    <meta http-equiv="description" content="This is my page">
    <!--
    <link rel="stylesheet" type="text/css" href="styles.css">
    -->
  </head>
  <body>
    <form action="buy.jsp">
              書籍：<input type="checkbox" name="item" value="book">
              電腦：<input type="checkbox" name="item" value="computer">
              汽車：<input type="checkbox" name="item" value="car">
     <input type="submit" value="提交">
    </form>
    <h1>在線用戶：</h1>
    <table>
       <tr>
          <td>ID</td>
          <td>名稱</td>
       </tr>
       <%
          HashMap<String,String> online=(HashMap<String,String>)application.getAttribute("online");
          for(String sessionId:online.keySet()){
        %> 
        <tr>
           <td><%=sessionId%></td>
           <td><%=online.get(sessionId)%></td>
        </tr>
        <%
          }
       %>
    </table>
  </body>
</html>

三、使用RequestListener更精確監控用戶在線狀態

1、實現ServletRequestListener
package listener;
import java.sql.ResultSet;
import java.sql.SQLException;

import javax.servlet.ServletContext;
import javax.servlet.ServletRequestAttributeEvent;
import javax.servlet.ServletRequestAttributeListener;
import javax.servlet.ServletRequestEvent;
import javax.servlet.ServletRequestListener;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;

import dao.DbDao;
public class RequestListener implements ServletRequestListener,ServletRequestAttributeListener{
    //當請求銷燬時觸發該方法
    public void requestDestroyed(ServletRequestEvent sre) {
        // TODO Auto-generated method stub
        HttpServletRequest request=(HttpServletRequest)sre.getServletRequest();
        System.out.println("----發向"+request.getRequestURI()+"被銷燬");

    }
    //當請求初始化時觸發該方法
    public void requestInitialized(ServletRequestEvent sre) {
        // TODO Auto-generated method stub
        HttpServletRequest request=(HttpServletRequest)sre.getServletRequest();
        System.out.println("---發向"+request.getRequestURI()+"被初始化");
        HttpSession session=request.getSession();
        //獲取sessionId
        String sessionId=session.getId();
        //獲取IP與地址
        String ip=request.getRemoteAddr();
        //獲取正在訪問的頁面
        String page=request.getRequestURI();
        //獲取用戶名稱
        String user=(String)session.getAttribute("user");
        user=(user==null)?"遊客":user;
        DbDao db=new DbDao("com.mysql.jdbc.Driver","jdbc:mysql://localhost:3306/escshop", "root", "");
        ResultSet rs=db.query("SELECT * FROM online_information WHERE sessionId=?", true, sessionId);
        try {
            if(rs.next()) {
                 rs.updateString(4, page);
                 rs.updateString(5,String.valueOf(System.currentTimeMillis()));
                 rs.updateRow();
                 rs.close();
            }else{
                db.insert(sessionId, user, ip, page, String.valueOf(System.currentTimeMillis()));
            }
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }
    //當新增屬性時觸發該方法
    public void attributeAdded(ServletRequestAttributeEvent srae) {
        // TODO Auto-generated method stub
        ServletContext request=srae.getServletContext();
        String name=srae.getName();
        Object value=srae.getValue();
        System.out.println(request+"範圍內新增了屬性名爲name="+name+"\t"+"屬性值爲value="+value);
    }
    //當移除屬性時觸發該方法
    public void attributeRemoved(ServletRequestAttributeEvent srae) {
        // TODO Auto-generated method stub
        ServletContext request=srae.getServletContext();
        String name=srae.getName();
        Object value=srae.getValue();
        System.out.println(request+"範圍內移除了屬性名爲name="+name+"\t"+"屬性值爲value="+value);
    }
    //當替換屬性時觸發該方法
    public void attributeReplaced(ServletRequestAttributeEvent srae) {
        // TODO Auto-generated method stub
        ServletContext request=srae.getServletContext();
        String name=srae.getName();
        Object value=srae.getValue();
        System.out.println(request+"範圍內替換了屬性名爲name="+name+"\t"+"屬性值爲value="+value);
    }
}

2、實現ServletContextListener監聽器
package listener;

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.sql.ResultSet;
import java.sql.SQLException;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.swing.Timer;

import dao.DbDao;

public class OnlineRequestListener implements ServletContextListener{
    //超過10分鐘沒訪問則判斷已經離線
    public final int MAX_MILLITS=10*60*1000;
    //應用銷燬時執行此方法
    public void contextDestroyed(ServletContextEvent arg0) {
        // TODO Auto-generated method stub

    }
    //應用啓動時執行此方法
    public void contextInitialized(ServletContextEvent arg0) {
        // TODO Auto-generated method stub
        //每5秒檢查一次啊
        new Timer(1000*5, new ActionListener() {

            public void actionPerformed(ActionEvent e) {
                // TODO Auto-generated method stub
                DbDao db=new DbDao("com.mysql.jdbc.Driver","jdbc:mysql://localhost:3306/escshop", "root", "");
                ResultSet rs=db.query("SELECT * FROM online_information");
                StringBuffer buff=new StringBuffer("(");
                try {
                    while (rs.next()) {
                        //如果距離時間超過上次訪問時間
                        if(System.currentTimeMillis()-Long.parseLong(rs.getString("time"))>MAX_MILLITS){
                            buff.append("'");
                            buff.append(rs.getString(1));
                            buff.append("' ,");
                        }
                    }
                    System.out.println("buff:"+buff);
                    //有刪除的記錄
                    if(buff.length()>3){
                        buff.setLength(buff.length()-3);
                        buff.append("')");
                        //刪除所有在指定時間內未訪問的用戶信息
                        String sql="delete from online_information where sessionId in"+buff.toString();
                        System.out.println("sql:"+sql);
                        db.delete(sql);
                    }
                } catch (SQLException e1) {
                    // TODO Auto-generated catch block
                    e1.printStackTrace();
                }
            }
        }).start();
    }
}

3、數據庫操作
package dao;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class DbDao {
    private String driver;
    private String url;
    private String user;
    private String password;
    //構造方法
    public  DbDao(String driver,String url,String user,String password){
        this.driver=driver;
        this.url=url;
        this.user=user;
        this.password=password;
    }
    //查詢指定ID信息
    public ResultSet query(String sql,boolean flag,String id){
        ResultSet rs=null;
        try {
            Class.forName(driver);
            try {
                Connection conn=DriverManager.getConnection(url, user, password);
                Statement smt=conn.createStatement();
                if(flag){
                    sql=sql.replace("?","'"+id+"'");
                }
                rs=smt.executeQuery(sql);
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return rs;
    }
    //查詢所有信息
    public ResultSet query(String sql){
        ResultSet rs=null;
        try {
            Class.forName(driver);
            try {
                Connection conn=DriverManager.getConnection(url, user, password);
                Statement smt=conn.createStatement();
                rs=smt.executeQuery(sql);
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return rs;
    }
    //插入信息
    public boolean insert(String sessionId,String userName,String ip,String page,String time){
        boolean flag=false;
        try {
            Class.forName(driver);
            try {
                Connection conn=DriverManager.getConnection(url, user,password);
                Statement smt=conn.createStatement();
                String sql="INSERT INTO online_information(sessionId,USER,ip,page,TIME)"
                          +"VALUES('"+sessionId+"','"+userName+"','"+ip+"','"+page+"','"+time+"')";
                System.out.println("SQL:"+sql);
                flag=smt.executeUpdate(sql)>0?true:false;
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return flag;
    }
    //刪除指定的目錄
    public boolean delete(String sql){
        boolean flag=false;
        try {
            Class.forName(driver);
            try {
                Connection conn=DriverManager.getConnection(url, user,password);
                Statement smt=conn.createStatement();
                flag=smt.executeUpdate(sql)>0?true:false;
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return flag;
    }
}


4、顯示在線人員狀態的JSP
<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%@page import="dao.DbDao"%>
<%@page import="java.sql.ResultSet"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">

    <title>online在線人數</title>

    <meta http-equiv="pragma" content="no-cache">
    <meta http-equiv="cache-control" content="no-cache">
    <meta http-equiv="expires" content="0">    
    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
    <meta http-equiv="description" content="This is my page">
  </head>
  <body>
    <h1>當前在線人員：</h1>
    <table>
    <%
       DbDao db=new DbDao("com.mysql.jdbc.Driver","jdbc:mysql://localhost:3306/escshop", "root", "");
       ResultSet rs= db.query("SELECT * FROM online_information");
       while(rs.next()){
    %>
      <tr>
         <td><%=rs.getString(1)%></td>
         <td><%=rs.getString(2)%></td>
         <td><%=rs.getString(3)%></td>
         <td><%=rs.getString(4)%></td>
         <td><%=rs.getString(5)%></td>
      </tr>
    <%} %>
    </table>
  </body>
</html>